At present, in the Thin Film Transistor-Liquid Crystal Display (TFT-LCD) field, a large-scale LCD panel is developing quickly with continuous updating of technologies. A Touch Panel (TP), as an input medium, is integrated with a display screen to form a touch display screen which plays an important role in the display field. Particularly, a capacitance touch panel is popular because of high sensitivity thereof. A mutual capacitance touch panel is commonly employed because of its advantages, such as high sensitivity and multi-touch detection capability.
At present, according to combination methods of the touch panel and an LCD device, there are two kinds of the touch panels, i.e., an on-cell touch panel and an in-cell touch panel. The on-cell touch panel and the display device are manufactured separately and then are assembled together. In this way, the thickness of the display screen will be increased. In addition, the transmittance and the contrast of the display will be reduced because multiple layers of transparent glasses or thin films are provided additionally. Further, the manufacturing cost is high with this method. Therefore, current research focuses on in-cell touch panel technology which integrates the TP into a touch liquid crystal display Panel (LCD Panel) because of its low production cost, high transmittance, and thin thickness, etc.
In a mutual capacitance touch panel, X-direction coordinates of touch points are determined by touch driving electrodes, and Y-direction coordinates of the touch points are determined by touch sensing electrodes. A touch driving voltage is applied to the touch driving electrodes. A constant voltage is applied to the touch sensing electrodes. For detecting a touch point, a progressive scanning is performed on the X-direction touch driving electrodes. When each row of the touch driving electrodes is scanned, the signal on each column of the touch sensing electrodes is read. Intersections of each row and each column can be scanned through a round of full-screen scanning to obtain X*Y signals. The coordinates of multiple touch points can be determined with this touch location detection method, and thereby the multi-touch detection can be realized.
FIG. 1 shows an equivalent circuit of a mutual capacitance touch panel, which includes a signal source 101, a touch driving electrode resistance 103, a mutual capacitance 102 between the touch driving electrode and the touch sensing electrode, a parasitic capacitance 104 between the touch driving electrode and a common electrode or between the touch sensing electrode and a common electrode, a touch sensing electrode resistance 105, and a touch point detection circuit 106. A part of the current of the circuit flows into a touch object (e.g., a finger) when the touch panel is touched by the touch object, resulting in a change of the value of the mutual capacitance 102 between the touch driving electrode and the touch sensing electrode. The touch point detection circuit converts the weak current changes caused by the mutual capacitance 102 into a output voltage signal Vout.
The touch driving electrode and the touch sensing electrode are both disposed on the LCD panel, and the distance between the TP and the common electrode of the LCD panel is very short. Thus, the parasitic capacitance 104 between the touch driving electrode and a common electrode or between the touch sensing electrode and the common electrode is very large, such that the TP is affected greatly by noises generated by the LCD panel. In this case, current signals detected by the touch point detection circuit are difficult to be detected due to the noises, and thus touch resolution is poor, as a consequence, the touch panel may not operate accurately.
In addition, considering conventional touch display panels, a signal current is small and easy to flow from the driving electrode to the sensing electrode when the touch signal strength is weak. Thus, a signal delay exists between a peripheral side and the center of the common electrode, which will cause the signal at the center of the TP to be weaker than that at each of the four sides thereof. In this case, the signal detection of the TP is affected, and there is a problem that the touch signal will not be detected.